Air conditioning systems are currently commonplace in homes, office buildings and a variety of vehicles. Over time, the refrigerant included in these systems becomes depleted and/or contaminated. As such, in order to maintain the overall efficiency and efficacy of an air conditioning system, the refrigerant included therein is periodically replaced or recharged.
Refrigerant recovery units are used in connection with maintaining and servicing refrigeration circuits. The portable machines include hoses coupled to the refrigeration circuit to be serviced. A compressor operates to recover refrigerant from the air conditioning system, flush the refrigerant, and subsequently recharge the system from a supply of either recovered refrigerant and/or new refrigerant from a refrigerant tank.
Due to the nature of portable refrigerant recovery units, the pistons within the unit compressors of the recovery unit do not form a perfect seal with the cylinder side wall. For this reason, compressed refrigerant leaks through the piston rings into the compressor case. In some compressors, the compressor case is open to atmosphere, and any refrigerant leaking into the case is lost. After significant use, the piston rings can become worn or damaged leading to an increased rate of leakage, and the lost refrigerant can become a substantial amount. This can lead to increased cost of recovery to replace the lost refrigerant.
In some compressors, the compressor case is sealed, and includes a passage between the compressor case and the inlet of the compressor, called a “bleedback hole,” to allow refrigerant within the case to escape back to the inlet. The bleedback hole also allows pressure from the low-side inlet to freely enter the crank case. Pressure in the crank case increases the efficiency of the compressor, since the pressure acts on the pistons of the compressor to assist in the compression stroke of the piston. However, the efficiency increase due to only low-side pressure entering the crank case is minimal. Once running, this small amount of pressure within the crank case becomes negligible as the source tank or system supplying the pressurized refrigerant depletes.
Furthermore, systems having a bleedback hole do not allow control or selection of the pressure in the crank case. The bleedback hole is perpetually bleeding pressure between the compressor inlet and the crank case. This also makes it difficult for the compressor to produce a vacuum on the air conditioning system being serviced at the end of the recovery operation, as a certain amount of refrigerant will continue to flow through the bleedback hole.
What is needed, therefore, is an improved compressor for a refrigerant recovery unit having increased efficiency and reduced refrigerant losses.